1. Field of the Invention
The invention relates generally to electromagnetic antenna systems, and more particularly, to wideband antenna systems including plural individual arrays employable for such purposes as direction finding, polarization determination, etc.
2. Description of the Prior Art
In the prior art, antenna systems for the general problem of signal surveillance and analysis have taken a number of forms. In general, where there usually is a requirement for signal surveillance over a large band of frequencies. Systems involving log-spiral antennas and the like, have been known and used. Those particular prior art devices, and other known prior art devices for the purposes, have presented disadvantages, particularly in size and flexibility. The spirals, for examples, must be on the order of a full wavelength in diameter to provide satisfactory operation in more than a single mode. A mode for the purpose of this specification is, for example, a direction finding mode, a polarization determining mode, etc.
In many applications, such as in connection with airborne or spaceborne platforms, the size of the antenna structure and its weight are critical considerations, especially if operation in lower frequency bands is required.
In addition, many prior art multiband, multimode antenna arrangements do not have the ability to discriminate against electromagnetic energy arriving at angles widely separated from the antenna boresite. This is particularly true of antennas of the spiral type, since the antenna aperture size is larger for the secondary than the primary mode of radiation, and therefore the higher modes lie within the beamwidth of the primary mode.
Still further, the spiral antenna structure and other prior art structures preclude, in general, the ability to make clear determination of polarization characteristics of arriving signals to be analyzed.
The manner in which the present invention solves the problems of the prior art in an unique combination providing wideband multimode operation in a relatively small and lightweight assembly, will be understood as this description proceeds.